加氢高压空冷系统腐蚀原因分析与对策

ANALYSIS OF CORROSION OF HIGH-PRESSURE AIR COOLERS IN HYDROPROCESSING UNIT AND COUNTERMEASURES

在调研中国石化集团多套加氢高压空冷系统腐蚀情况的基础上,分析其具有腐蚀难于控制、普遍存在、空冷器泄漏危险性大且制造质量不易保证的特点,由于实际原料中S和N含量高,而设计的空冷系统处理量不足;原设计无循环脱硫设施;注水量难以随着原料改变而提高;空冷器流速过高、物流分配不均;操作不平稳等原因造成腐蚀。提出了以Kp值划定腐蚀环境,控制反应流出物中过高Cl^-含量,高压空冷器材质使用碳钢或Incoloy825,考虑控制介质流速的上下限和高分水的铵盐含量等六条腐蚀控制原则。提出了工艺设计,高压空冷器材料和结构设计以及制造,管道设计和平面布置的建议,同时建议操作中应定期检测工艺参数,保证任何工况下高压空冷器前注水点大于25%的未汽化水和冷高分水中的铵盐质量分数为4%～8%,空冷器风机应全开,冬季空冷器出口温度不能过低。

On the basis of investigation of a number of hydroprocessing units in SINOPEC＇ s petroleum refineries and petrochemical plants, the greater leakage hazards and difficulty to control the fabrication quality of high-pressure air coolers are analyzed. It is found that the corrosion in air cooler system is caused by higher S and N in unit feedstock, inadequate air cooler capacity, unavailability of facility for recycle desulfurization in original design, inability to increase the amount of injection water with the variation of feedstocks, excessive flow velocity of coolers and mal-distribution of effluents and unstable operation etc. Six corrosion control measures are suggested, such as classification of corrosive environment based upon Kp value, control of excessive Cl^- in reaction effluent, selection of carbon steel or Incoloy825 steel for high-pressure coolers, control of upper and lower limits of flow medium velocity and ammonium salts in high pressure separator water etc. In addition, improvements in process design, material selection, construction design and fabrication of high-pressure air coolers as well as associated piping design and plot plan are proposed. It is also recommended that the process parameters be inspected regularly in operation to ensure that a minimum 25% of water phase is maintained at the water injection point upstream of the air coolers and the ammonium salts in high-pressure separator water is controlled at 0.4 m% - 0.8 m% at all operating modes. All fans in air coolers should be turned on and excessive low outlet temperature of coolers should be prevented in winter.